For the purpose of obtaining good black-and-white monochrome images and gray scale by an inkjet recording method or the like, there are sometimes used an ink set containing at least three black inks different in concentration of a black pigment (i.e., carbon black). For example, by using three black inks different in carbon black concentration, stability of gray balance and metamerism are dramatically improved. Particularly, the effect is very large in terms of gray balance. Namely, this is because graininess in a high-tone region (bright region) is overcome, which is problematic in the case that gray balance is outputted with only one or two black inks.
An image recording apparatus using plurality of black ink compositions different in carbon black concentration and a set of color ink compositions in combination and a controlling method thereof have been already known (Patent Document 1). However, the technology described in Patent Document 1 aims at formation of monochrome high gradation images in addition to color images on the same recording medium, and it merely disclose the use of plurality of black ink compositions in order to form the monochrome high gradation images.
Moreover, an ink set containing three or more black inks different in black dye concentration have been hitherto known and also offered commercially.
Patent Document 1: JP-A-11-320924
In the case that the colorants of the three black inks are all black dyes, there is a problem in respect of short-term color stability. Namely, since a phenomenon of gradual color change after output from a printer onto a recording paper is induced, the quality is insufficient for monochrome print where strict color accuracy is required.
On the other hand, in the case that the colorants of the three black inks are all black pigment (i.e., carbon black), print quality is high and particularly there is no problem in short-term color stability but there are problems in respect of increased complexity of composition and in respect of gloss. Namely, in the case that recording is carried out using a black ink composition low in carbon black concentration, in recorded images, at the time when a fluorescent lamp, an outside light, or the like is reflected by recorded images, there is a problem that the reflected light generates gold-like gloss. Moreover, in the case that recording is carried out using a black ink composition for medium gradation having medium concentration, there is a problem that there is generated a part where gray lightness shifts.